1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof in which a volume efficiency is improved, and more particularly, to a solid electrolytic capacitor for improving a contact structure of a capacitor element and a lead frame such that the capacitor element has a greater volume to improve the volume efficiency.
2. Description of the Related Art
Generally, a solid electrolytic capacitor called a tantalum capacitor is widely used in an application circuit having a low rating voltage range as well as in a general industrial device, and in particular is widely used in a circuit in which a frequency characteristic is of question. Generally, the solid electrolytic capacitor is widely used to reduce a noise of a portable communication device.
As shown in FIG. 1, a conventional tantalum capacitor 100 includes a capacitor element 102 embedded into a case 112; an anode lead wire 108 integrally protruded from the capacitor element 102; an anode lead frame 104 welded to the anode lead wire 108 and protruded out of the case; and a cathode lead frame 114 being in contact with the capacitor element 102.
A method of manufacturing the capacitor 100 includes performing a press step for cuboid-shaping and sintering a dielectric powder; performing a chemical step for forming a dielectric coating film on an outer surface of the resultants; and dipping the resultants in an aqueous solution of manganese nitrate to form a solid-electrolytic manganese dioxide layer on an outer surface of the resultants by using thermal decomposition.
Recently, the tantalum capacitor 100 is widely used in a miniaturized device to be in a tendency of gradual miniaturization comparing to the conventional art. If the capacitor 100 is miniaturized, contact portions of the capacitor element 102 and lead frames 104 and 114 occupy much space to cause the tantalum element 102 to be small-sized relatively. As a result, the conventional tantalum capacitor has a drawback in that the capacitor element has a small volume efficiency to reduce capacitance and increase impedance.
Further, since the lead frame is required to be much limited in reduction of a size itself so as to firmly fix the lead frame inserted into the case, the lead frame inserted into the case should be much limited in size reduction. That is, it is required to firmly fix the lead frame by molding; if the lead frame is excessively reduced in size, there is a drawback in that the lead frame is not firmly fixed.
FIG. 2 illustrates the tantalum capacitor for increasing the volume efficiency of the capacitor element by improving the contacting method of the lead frame. FIG. 2 relates to U.S. Pat. No. 6,262,878 entitled as “Chip Capacitor”.
In FIG. 2, the capacitor element 200 has a cathode layer 220 on its outer surface, and has an anode lead wire 240 protruded from its body. Further, on one lower end of the cathode layer is formed a flat-shaped cathode lead frame 210 parallel with and electrically connected with the cathode layer, and on the other lower end of the cathode layer is formed a flat-shaped anode lead frame 230 electrically connected with an anode connection member 234.
The conventional chip capacitor is constructed to arrange the lead frames on a lower surface of a chip so as to increase the volume efficiency of the capacitor element of the chip, and to connect the lead frame with an external terminal. However, the above structured chip capacitor can achieve an advantageous increase of the volume efficiency, whereas has a drawback generated when the chip is mounted.
In other words, since the chip has the terminal only at the lower surface thereof, the chip does not have the terminal at the side surface thereof. Accordingly, at the time of soldering, the conventional chip capacitor has a drawback in that the contact area between the solder and the terminal is not formed normally. The solder 270 is bonded to the chip in a shape as in FIG. 3. The solder 270 is used to bond the cathode lead frame 210 disposed on the lower surface of the solid electrolytic capacitor to a substrate 290, and most of the solder 270 is bonded to the side surface of the chip. This causes unreliability in the electrical connection of the chip and the substrate.